Electrical drive for scanning optics in a continuously variable reduction copier

ABSTRACT

A scanning continuously variable reduction electrophotographic copier includes a servo motor for driving the document scanning carriages. Servo motor, and therefore carriage motion parameters of velocity, duration of acceleration and deceleration, length or time duration of travel and time of start of scan are selectable to produce a selected reduction ratio within a continuous range of reduction ratios. In one embodiment, three partially overlapping hybrid servo loops are used, one for acceleration and deceleration, another for constant velocity motion and a third for precise stopping control. In another embodiment, a single loop controls the entire motion.

FIELD OF THE INVENTION

The present invention relates to an electrical drive system for thescanning carriage in a continuously variable reduction electrostaticcopier.

RELATED APPLICATIONS

The present invention provides an electrical drive for the scanningcarriage in a copier which, in other respects, is disclosed inapplication Ser. No. 904,706 filed May 10, 1978 which is a continuationof now-abandoned Ser. No. 721,125 filed on Sept. 7, 1976, commonlyassigned, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

In most known electrophotographic copy machines, an image of the objectbeing copied is directed to an image carrier. The image can be of theentire document (a flash exposure system) or of only a portion of thedocument (a scanning system). In the latter case, an image of thedocument is built up in time as the object being copied is scanned.

Scanning systems have been embodied in plain and coated paper copiers.In the former type, the image is electrically recorded on anintermediate carrier from whence it is transferred to the copy paper. Inthe latter type, the image is directly laid down on the coated paper.Accordingly, the term image carrier will be applied to either theintermediate carrier (for plain paper copiers) or the copy paper (forcoated paper copiers).

Various document copier machines have been produced with the capabilityof reducing the size of copies made from an original, usually placed ona transparent document support. Most of these machines, however, havebeen designed for providing specific discrete reduction ratios, e.g.,0.75:1 or 0.6:1. Rarely has an attempt been made to provide a documentcopier with the capability of continuously variable reduction fromratios such as 1:1 to another ratio such as, for example, 0.647:1. Thefew attempts that do appear in the prior art, for example. U.S. Pat.Nos. 2,927,503 (Zollinger) and 3,395,610 (Evans) have operated with aflash exposure system. Flash exposure systems have the disadvantage ofrequiring a flat imaging surface which thus cannot use the rotatingimage carrier, or drum, found in the most popular commercially availablecopying machines. The requirement of a flat image plane also requires amechanically more complex machine which occupies more space than does amachine which employs the rotating drum. Other disadvantages of theflash system are a higher power requirement and a machine which cantemporarily blind an operator if the flash is eye-observed. Despitethese disadvantages, most prior variable reduction systems opt for theflash exposure procedure to take advantage of the simplicity of itsconcept. For example, one of the complexities of the scanning system ina reduction copy machine is a requirement that the velocity of thescanning carriage relative to the surface velocity of the image carrierbe changed as the reduction ratio is changed. However, systems capableof this function exist in the prior art, for example, U.S. Pat. Nos.3,614,222; 3,897,148; and 3,542,467, but these systems are limited totwo, three and five discrete reduction ratios, respectively, andtherefore, only require two, three or five velocity ratios.

Since the carriage cannot be accelerated instantaneously, each carriagemovement may include six phases. A scan movement is accomplished from astart of scan position to a home position encompassing acceleration,constant velocity and deceleration phases. Image transfer isaccomplished during the constant velocity phase. This phase is onlynominally at constant velocity since the objective is to maintainconstant the relationship between carriage velocity and image carriervelocity. The carriage must also be moved from the home position to thestart of scan position (termed rescan) which movement may also encompassthree similar phases of motion.

In addition to selecting scan velocity, of the "constant" velocity phaseof movement, in a manner correlated with a selected reduction ratio, thelength of the scan must also be selected. For example, at 1:1, an 11inch document is scanned into an 11 inch image, but at 0.647 reduction,a 17 inch document is scanned into the same 11 inch area. Thus, not onlymust the scan velocity be appropriately selected, but also the length ofthe scan. Of course, of primary concern is the length of the "constant"velocity phase. However, different velocities require different travellengths for acceleration and deceleration as well.

In addition to selection of scan velocity and length, the relativeposition of the leading edge must also be located. Desirably, theleading edge of the copy paper must be matched to the leading edge ofthe image area. Therefore, if both the document and the copy paper are81/2×11, it is necessary to place the leading edge of the image at theleading edge of the image area in order to transfer the entire image tothe copy paper. If a document of 17 inch size is placed on a documentsupport, it must still be squeezed into an 11 inch image area fortransfer to an 81/2×11 inch sheet of copy paper. Therefore, unless overreduction is practiced, the leading edge of the image of the reduceddocument must also fall on the leading edge of the image area.Furthermore, in a scanning system, the carriage must scan the documentat a velocity selected in dependence on the desired reduction. Thedifferent velocities require different acceleration times (anddistances) and thus, the position of the carriage at the beginning ofits movement and the time the movement commences relative to the imagearea on the drum must also be properly selected. Accordingly, thescanning carriage position at the beginning of movement must be selectedin terms of time or space (or both) so that the carriage begins to scanthe document at the same position relative to the image carrier surface,regardless of reduction.

The referred to patent application discloses a scanning, continuouslyvariable reduction photocopier which meets the heretofore statedobjectives of altering scan velocity, scan length and starting documentscan location. In the referred to patent application, however, thescanning carriage drive system is mechanically coupled to the main drivemotor and various cams, lead screws and drive bands are selectivelypositioned, rotated or adjusted so as to produce the desired motion.However, we believed it desirable to provide a system meeting theseobjects in which the scanning carriage drive was electricallycontrolled, rather than being mechanically coupled to the main drivemotor. By providing an electrical control for the scanning carriagedrive a number of advantages are derived. For one thing, the main drivemotor can be reduced in size and the previously noted mechanicallinkages can be eliminated, thus significantly reducing the totalrequired machine drive torque, total machine volume and significantlyreducing mechanical part count. In one embodiment, this torque reductionwas over 30%, machine volume decreased by 500 in³ and the mechanicaldrive part count was reduced from over 300 to about 60.

Since the carriage drive is no longer mechanically coupled to the maindrum motor, flexibility is provided in selecting the relative timing ofvarious machine cycles and this allows a reduction in the "time to firstcopy" which is an important characteristic of copying machines.

In addition, decoupling carriage drive and main motor drive enablescarriage motion to adapt for different paper lengths maintaining acommon image reference to both simplify gating paper feed andeliminating detack marks from within the image area since the paperdetack is common for all lengths of paper. Furthermore, mechanicalcouplings to the optical elements (lens and carriage positioning) can beeliminated significantly simplifying the optical controls. The overallsimplification of the machine, reduction in number of components andmachine volume, and decrease in power requirements will lead to asignificant reduction in required maintenance.

SUMMARY OF THE INVENTION

Briefly stated, the invention comprises a continuously variable reducingimaging system for an electrophotograph copy machine which employsscanning optics for directing the image to the image carrier and inwhich the scanning optics are electrically, not mechanically, coupled tothe main drive motor. More particularly, the scanning carriage drive isservo controlled. To meet the requirements of providing continuouslyvariable reduction ratios, scanning velocity is uniquely selected amonga continuous range of velocities so as to provide the proper relationbetween image carrier velocity and scanning velocity. To maintain thedesired relationship between scanning carriage velocity and imagecarrier velocity, in view of the lack of any mechanical coupling betweenthem, a servo loop is employed to "phase lock" the scanning drive motorto the motion of the image carrier. Unique scanning velocities, eachrelated to a different reduction ratio, are achieved by accelerating theservo motor. Accordingly, the acceleration time to achieve differentvelocities is also different. As a consequence, since the variousdocuments to be copied have a common reference edge, the scanningcarriage may begin its acceleration at a unique position correspondingto each of the different unique velocities which are to be achieved.

Mechanically decoupling the scanning carriage drive from the main drivemotor allows the scanning carriage drive to be energized independent ofimage carrier motion. This is advantageous particularly in systems whichemploy a drum as the image carrier. More particularly, the scanningcarriage is no longer limited to beginning motion at a selected positionin the rotation of the drum. This allows the image from various sizeddocuments to be laid down on the drum with a common leading edge whichis advantageous in that it eliminates detack marks on copy paperproduced by the detack of previously made smaller-sized copies.

In one embodiment, the copier includes a stationary document glass and arotating photoconductive drum. The scanning carriage is driven by aservo motor which, at various times, is controlled by one of a pluralityof feedback loops. The feedback loops can be conditioned in accordancewith a desired reduction mode in a continuous range of reduction modes.Operator controls adjusted to select a particular reduction mode arereflected within the machine by positioning a lens at a unique positionalong a predetermined path, the position corresponding to the desiredreduction mode. The scanning carriage assembly includes, as is shown inthe referenced application, a pair of scanning carriages whose positionrelative to each other is adjusted in accordance with the desiredreduction mode to maintain constant total conjugate length. The selectedreduction mode, in a continuous range of reduction modes, determines aunique trajectory (in scan and rescan movements) for the scanningcarriage assembly comprising the pair of carriages. The trajectoryconsists of acceleration, deceleration, constant velocity and stoppingphases. The feedback loops referred to hereinbefore control the servomotor driving the scanning carriage assembly based upon the selectedreduction mode, one loop operating at least in an acceleration phase andanother operating in constant velocity phase of carriage motion.

Both feedback loops monitor the servo motor drive so as to derive bothposition and velocity information for the scanning carriage. The totallength of the scanning carriage drive assembly movement, selected independence upon the desired reduction mode, is stored in a positioncounter, and decremented as the servo motor drives the scanning carriageassembly. At various times during the acceleration phase of the scanningcarriage drive assembly movement, the actual position of the scanningdrive assembly is compared to the theoretically desired position for thescanning carriage drive assembly at that point in time. The error isemployed in a first feedback loop to modify a substantially constantcurrent provided to the servo motor for accelerating the scanningcarriage assembly. As the scanning carriage drive assembly reaches theend of its acceleration phase, the comparison is terminated and a secondfeedback loop is enabled to control the constant velocity portion of thescanning carriage drive assembly movement. In this feedback loop, servomotor velocity is compared with main drum motor velocity so as tomaintain a constant ratio, which ratio is selected in accordance withthe desired reduction mode in a continuous range of reduction modes. Theposition of the scanning carriage drive assembly throughout the constantvelocity phase of its trajectory is monitored and, as the constantvelocity phase terminated, the first mentioned feedback loop may againbe enabled and the second feedback loop is disabled to provide fordeceleration of the scanning carriage drive assembly in a controlledmanner. In a varient on this first embodiment of the invention,deceleration is open loop.

The variables of scan length, scan speed and relative scan time can berelated in a number of ways within the scope of the invention. Forexample, assuming fixed acceleration, the time to reach variousvelocities or velocity ratios is different, however, the time at whichimage transfer begins must be constant relative to drum motion to insurethat the image occupies the identical image area regardless of reductionratio. The beginning of carriage movement, relative to drum position,can be different for each of the various reduction ratios to insure thatthe image, laid down in the constant velocity phase of carriage motion,appears at the proper location on the drum. This can be implemented bydelaying start of carriage motion uniquely for each reduction ratio.

The necessity for such unique delay can be eliminated, however, byaltering the location from which motion starts so that the motion startsat the same time relative to drum position for all reduction ratios.Since 1:1 or lower reduction ratios require lower velocity than higherreduction ratios, the carriage will come up to scan velocity earlier for1:1 or low reduction ratios. This is compensated for by merelylengthening the constant velocity phase of travel by the distancetravelled at constant velocity in excess of that required for copying.With this technique, the unique delays for start of scan at differentreduction ratios can be eliminated.

In another embodiment of the invention, carriage motion is controlled bya single control loop throughout the different phases of motion. Thedriving force in the loop is obtained by the pulse outputs of a counteron overflow (or underflow), each such pulse representing a fixed extentof travel. The counter is cycled by a clock, phase locked to the imagecarrier motion. The loop controls both velocity and position of thecarriage motion through the agency of a device for selectivelypresetting the counter in a unique pattern related to each desiredreduction mode and corresponding to unique carriage trajectories. Thatis, at the beginning of motion the counter may not be preset so thepulse output is produced at a low rate related to only image carriermotion. As the carriage picks up speed, however, the counter is presetto different positions so the pulse output rate is increased. Carriageposition changes are used to decrement a second counter which isincremented by the pulse output so that real time position error isreflected by the contents of the second counter. The D to A convertedoutput of the second counter drives the servo motor. The presettingpattern of the first counter is selected so that carriage motion reachesdesired velocity at the proper position and time. Thereafter, bymaintaining constant the presetting of the first counter a steady statecondition is reached providing for constant velocity motion. In similarfashion, the carriage can be decelerated to a stop by continuing withthe presetting pattern. Since the presetting pattern for any reductionratio is precalculated to achieve the desired trajectory, merelyselecting the pattern and initiating operation when the carriage andcarrier are in known positions results in the carriage describing thedesired motion with respect to the carrier. Since the loop keeps trackof carriage position to a tolerance less than the movement correspondingto a single output pulse, motion is repeatable to within the sametolerance.

In the preceding discussion, phrases such as reduction ratios selectedwithin a continuous range of ratios or velocities selected in acontinuous range of velocities have been used. The selected reductionratio is determined by lens position. Since lens position is determinedor measured in a digital fashion, there is not, in absolute terms, acontinuous range of ratios, but, in fact, only those ratios whichcorrespond to a discrete (digital) measurement of lens position.However, the large number of such positions (for example, ninety)results in a copier which, for all practical purposes, possesses acontinuous range of reduction ratios, since the reduction range of1:0.647 is divided into ninety steps. In practical effect, the largestnon-unity ratio is 0.992812 and the smallest non 0.647 ratio is0.654188. Thus, in practical terms, the difference between a machinewith an absolutely continuous range of reduction ratios and the machinesdisclosed herein is the fact that only ninety reduction ratios areavailable rather than a theoretically infinite number. The ninetyratios, however, are in practical effect continuous since the eye cannotdiscern the difference between a reduction ratio of 0.992812 and anon-unity but higher ratio, for example.

In the preceding duscussion, and in preferred embodiments to bedisclosed hereinafter, the feedback loop detects servo motor velocityand position, although, of course, it is the scanning carriage driveassembly motion which is being controlled. Those skilled in the art willperceive that it is not necessary to monitor the servo motor, andinstead, the scanning carriage drive assembly position itself can bemonitored. In addition, since both the controlled object, that is, thecarriage drive assembly, and in some phases, the operation of thecontrolling source, i.e., the drum motor, are mechanical components, theelectrical control system must take into account the characteristics ofthese mechanical components. More particularly, the servo loop shouldinsure that the error or control signal does not excite the scanningcarriage drive assembly at a resonant frequency. This is effected in apreferred embodiment of the invention by limiting the control signals tofrequencies less than (and actually substantially less than) theresonant frequency of the scanning carriage drive assembly. In thepreferred embodiment to be disclosed hereinafter, electrical signals inthe frequency region above 30 Hz. are attenuated. Because the main motoris intended to be driven by a commercial power source, i.e., forexample, 60 Hz. , one can expect a relatively strong 60 Hz. component inthe drum motion, and indeed, such motion is normally found. Since thismotion is above the frequency at which control signals are attenuated,the scanning carriage assembly is not corrected for perturbations atthis frequency. To overcome this potential problem, the drum is actuallydriven through a "soft" coupling from the main motor. The soft couplingis actually a rubber or rubber-like section of the drive shaft whichdamps the 60 Hz. perturbations in the shaft motion. The use of thistechnique is not, however, essential, for if the scanning carriageassembly resonant frequency can be increased substantially above 60 Hz.,the control loop may follow perturbations at this rate, thus eliminatingthe need for this coupling.

Thus, in accordance with the invention, the scanning electrophotographiccopying machine is provided for copying at substantially any reductionratio within a range of reduction ratios comprising:

a motor,

image carrier means driven by said motor for recording a latent opticalimage thereon,

a transparent document support,

a lens,

reduction means for positioning said lens between said support and saidimage carrier means at a unique position corresponding to a selectedreduction ratio within said range,

scanning carriage means for scanning said document support and fordirecting an image beam from said document support to said lens, and

servo motor means responsive to said reduction means for driving saidscanning carriage for movement uniquely selected in accordance with saidreduction ratio.

In a first embodiment of the invention, the servo motor is alternatelycoupled to plural, partially overlapping feedback loops. The firstfeedback loop is employed during acceleration phase and may be employedin deceleration phase of scanning carriage assembly motion, and duringthese phases, plural corrections can be made for errors between scanningcarriage assembly position and theoretically desired position. Thesecond feedback loop is operative during constant velocity phase of themotion and in effect, maintains a constant ratio between the carriagevelocity and the carrier velocity for each reduction mode in a range ofreduction modes. Finally, a third feedback loop can be used for preciseposition control at the conclusion of scan.

In another embodiment of the invention, only a single control loop isemployed, a servo motor is employed to drive a scanning carriageassembly, and the motor is driven by the output of a bi-directionalcounter, the counter may be counted in one direction in response toservo motor feedback signals and is counted in an opposite direction inresponse to driving pulses, so that the bi-directional counter maintainsa real time count of scanning carriage assembly position error. Thedriving pulses are produced by the overflow (or underflow) of a firstcounter which is cycled or clocked at a rate controlled by the motion ofthe image carrier.

The first counter may be preset in a predetermined pattern so that thedriving pulses produced in overflow or underflow are produced inaccordance with the desired velocity of the scanning carriage assembly.The pattern of presetting is predetermined for each of a plurality ofreduction ratios in the range of reduction ratios so that each differentpresetting pattern produces a different velocity trajectory for thescanning carriage assembly and correspondingly produces movement of thescanning carriage assembly over a different unique distance where eachdistance is uniquely selected in accordance with a selected reductionratio.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings referred to herein, identical apparatus is identified byidentical reference characters and

FIG. 1 is a block diagram of the invention;

FIG. 2 is a partially broken away illustration of the optical path andassociated components;

FIG. 3 shows the scanning carriage assembly and the manner in which itis driven;

FIG. 4 shows operation of the reduction mode indicators 91, 93;

FIG. 5 illustrates interrelation of lens positioning and scanningcarriage positioning;

FIG. 6 illustrates plural velocity profiles;

FIGS. 7-10 relate to a first embodiment wherein:

FIG. 7 is a part schematic, part block diagram of the control 15;

FIG. 8 is a schematic of Interface 100;

FIGS. 9a-9c are a flow diagram of processor operation;

FIG. 10 is a block diagram of the reference clock;

FIGS. 11-14 relate to a second embodiment wherein:

FIG. 11 is a block diagram of the control 15;

FIG. 12a is a schematic of clock 401 and FIG. 12b shows representativewaveforms;

FIG. 13 is a schematic of load logic 402 and counter 403; and

FIG. 14 is a schematic of sign and count logic, and bias up or downlogic.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a block diagram of preferred embodiments of the invention;in FIG. 1, major components or subsystems are shown in block diagramfashion, solid lines indicate mechanical couplings and broken linesindicate electrical couplings. A main motor 10 is connected through atransmission 11 for driving the image carrier 13 (which may be a drum)and to other major copier components 14. A lens positioning system 16positions the lens in response to operator command inputs at 17 via amotor 18. As the motor 18 changes lens position, indicators 91, 93provide the operator with information which indicates when changes inreduction ratio can be terminated. The same motor 18 provides carriagepositioning for total conjugate length to insure correct total conjugatelength as indicated by the coupling between the motor 18 and thescanning carriage assembly 12. As explained in the referencedapplication, total conjugate length must be adjusted as the reductionmode is changed. Finally, a control 15 responds to a variety of inputs(including lens tach 21, a carrier tach 22, a motor tach 23, and variousoperator input commands 17 such as the number of copies to be produced)to properly control the scanning carriage assembly 12 for documentreproduction. Control 15 develops an analog drive signal that is aninput to the power amplifier 410 that drives the optics scan motor 70a.Rotation of the optics scan motor is monitored by tach 23. The outputfrom tach 23 is fed back to control 15.

FIG. 2 illustrates the physical relation between the major componentsused in transferring an image from a document to the image carrier. Adocument to be copied, usually of rectangular shape, is placed on aglass platen or support 50. The document may be centered along areference edge or corner referenced. Regardless of how the document ispositioned, a scanning carriage assembly located under the documentglass, moves across the under surface of the document, exposing thedocument with a long rectangular and moving area of light henceforthreferred to as a moving line of light 45. The assembly includes a pairof carriages, one carrying a light source 40 and a reflector 41, as wellas reflectors 44, 46 and a second carrying the reflectors 47, 48. Thecarriages and the rails on which they travel have been deflected fromFIG. 2. The reflected image from the moving line of light is directedthrough an optical system including the reflectors 46-48 and a lens 9 toa reflector 49 and then to an image carrier 13 (hereinafter referred toas a rotating drum, the surface of which may be comprised of aphotodetecting material carrying electrical charge). The reflection fromthe moving line of light produces a line image 45' of the illuminatedportion 45 of the document. The speed relationship between the scanningcarriage assembly and the tangential velocity of the drum is constantand of a desired ratio (during image transfer) to give the desiredreduction, for example, a 1:1 speed ratio provides for a full sizereproduction. As a result of the scan, an electrophotographic latentimage of the document is produced on the photodetector. This image isthen passed through a developer station in which toner material isdeposited on the latent image causing the toner to adhere to certainareas of the photodetector and not to others, depending on whether ornot light has been transmitted to the drum discharging the electricalcharge previously placed thereon. In plain paper copiers, the developedimage is then passed through a transfer station where the image istransferred to a copy paper sheet. The copy paper is then passed througha fusing station wherein the toner is fused to the paper to permanentlyaffix the image. Meanwhile, the drum continues to rotate through acleaning station where residual toner charge is removed from the surfaceof the drum prior to beginning the next copy cycle.

In coated paper copiers, the same basic operation occurs except that thephotoconducting material is located on the copy paper itself.Accordingly, the speed of the scanning and the speed of the copy paperduring the image transfer process must be matched in the appropriateratio for the selected reduction. The present invention is applicable toboth plain and coated paper copiers.

In the typical electrophotographic plain paper copier, the leading edgeof the copy paper must be brought into juxtaposition with the drum atthe transfer station to coincide with the leading edge of the imagearea. If the document is to be copied at a 1:1 ratio onto a copy sheetof exactly the same size, it is also necessary to provide the leadingedge of the document image at the leading edge of the image area so thatthe entirety of the document can be transferred to the copy sheet. Thesame holds true when a larger document is being reduced so that theentire document image completely fills the image area of the drum.Typical document copier such as the IBM Copier II or Series III providesthe necessary mechanisms for timing the relationship of copy paperleading edge to image area in order to provide this function. The samefunction is performed in coated paper copiers except that the leadingedge of the copy paper must match the leading edge of the image.

FIGS. 2A and 2B and the associated text of the referenced applicationdescribe the need for TCL correction while FIGS. 4, 5 and the associatedtext describe how the respective carriages are positioned and moved toalter the TCL correction for various reduction ratios and to maintainthe correction throughout the scanning movement of the carriages. Theneed for TCL correction is identical in the present invention and thecorrection is achieved in a similar fashion. More particularly, FIG. 3is a schematic showing of a pair of carriages, a first carriage 60 and asecond carriage 61, which move across the document glass 50 to move theline of light from one end of the document glass to the other. Scanningcarriage 60 includes the source of illumination (not illustrated) andthe first mirror 46. The scanning carriage 61 carries the mirrors 47 and48. The two scanning carriages 60 and 61 are mounted for movement alongparallel rails (not illustrated) and are driven along the rails by beltsor bands 62 and 66. The first belt 62 comprises an endless belt which isconnected to an arm 72 of the first carriage 60. The endless belt 62 issupported over pulleys 63, 64 and 67, 68 and is driven by a drive pulley69 which itself is driven from the drive shaft 71 of a servo motor 70.Thus, the movement of carriage 60 is proportional to the rotation of thedrive shaft 71 as reflected by the ratios of the driving elements of thepulley 69. The carriage 61 is driven through a belt or band 66 whichextends from a ground point 73 over a pulley 65 supported on thecarriage 61 and which terminates at the arm 72 of the carriage 60.Because of the motion multiplying arrangement, which is shown in FIG. 3,the movement of the two carriages is not equal, but carriage 61 movesexactly one half the distance moved by carriage 60, and this maintainsthe total conjugate length constant as is taught in the first-mentionedapplication. In the remaining part of the application, the motion of thecarriage 60 will be referred to as a motion of the scanning carriagedrive assembly, it being understood that motion of the carriage 61,while not equal to the motion of the carriage 60, is related thereto. Ofcourse, other driving arrangements can be implemented well within theordinary skill, such as other composite cable and pulley arrangements,steel bands instead of the cables, or a nut and lead screw arrangement.

FIGS. 4 and 5 (the former reproduced from the aforementioned applicationand the latter somewhat modified) illustrate the scanning carriages 60and 61 (the rails on which these carriages ride are not illustrated forclarity) along with the lens 9 (likewise, the rails on which the lens 9rides are also not illustrated for purposes of clarity). Alsoillustrated in these Figures is apparatus for feeding back informationto the operator to inform him when the lens is correctly positioned forthe document intended to be copied. The document is positioned in thedocument glass in the manner shown in FIG. 4, at the reference corner.Positioning indicators 91 and 93 are moved simultaneously by theoperator to encompass the outer edges of the document in two dimensions.By observing the position of the indicators 91 and 93, relative to thedocument, the operator knows when he has the system adjusted such thatthe entirety of the document is encompassed by the indicators and willtherefore be transmitted to the document image area when he initiatesthe copying process. As shown in FIG. 5, indicating pointers 91 and 93are operated by optics positioning motor 18, a cable 88, pulley 125,cable 94 and pulley 95. If pulley 95 is rotated in direction D, thencable 96 rotates to move positioning indicator 93 in a direction toencompass a larger and larger document. Similarly, positioning indicator91 moves to encompass a larger document along the other dimension. Thepositioning indicators 91 and 93 may move at any selected ratiodepending upon the nominal sizes of paper most frequently copied.

Under operator control, therefore, the motor 18 is rotated in onedirection or another depending on whether or not a larger or smallerdocument is to be copied than the document size indicated by theposition of the indicators. Assuming a larger size document is to becopied, the motor is energized in a particular direction and theindicators 91 and 93 are moved accordingly. At the same time, the cable88 rotates the lens cam 89 which is coupled to the lens 9 for properpositioning thereof so that when the operator deenergizes the motor 18,the lens is properly positioned for the desired reduction. The requiredmotion of lens 9 as reduction mode is varied is adequately disclosed inthe referenced application.

The same movement of the cable 88 also provides for rotation of the cam90 which serves, as is disclosed in the aforementioned application, toadjust the ground point 73 so as to properly position carriage 61 forthe associated total conjugate length in accordance with the desiredreduction mode.

It should be apparent, therefore, that the operator control in locatingindicators 91 and 93 results in positioning the lens 9, and the carriage61 at a selected position within a continuous range corresponding to theselected reduction mode in a continuous range of reduction modes.

The remaining parameters to be adjusted to provide for continuousreduction are the scan length for the carriages, and the velocityprofile. In addition, in order to provide for coincidence between theleading edge of the document image and the image area on the drum,account must be made of the proper starting time of carriage motion,relative to drum position.

FIG. 6 illustrates the carriage assembly velocity profile (i.e.,velocity vs. time) for five different reduction modes in a continuousrange of reduction modes from 1:1 to 0.647:1. It is emphasized that thefive discrete profiles shown here are for illustrative purposes only,and that, depending upon the reduction mode selected and therefore thelens position, the apparatus is also capable of providing intermediatevelocity profiles not specifically illustrated.

As is apparent, each velocity profile has three distinct phases: anacceleration phase, a constant velocity phase and a deceleration phase.All the profiles of FIG. 6 illustrate carriage motion toward the "home",reference or rest position which is the scanning phase of machineoperation in which an image is written onto the drum. The "constantvelocity phase" is only nominally constant in that the velocity duringthis phase bears a specified relationship with the tangential velocityof the drum 13. Thus, in the 1:1 reduction mode, the scanning carriagevelocity is maintained equal to drum tangential velocity, and in othermodes, the scanning carriage velocity is the drum tangential velocitydivided by the reduction mode, and the mode is in a range of 1.0 to0.647. It should be noted that the constant velocity phase is, in extentof time duration, equivalent for all profiles.

Because some of the reduction modes provide for higher carriage velocitythan others, the carriage in these modes travels a greater distance inthe constant velocity phase than the distance covered during theconstant velocity phase in the 1:1 mode. Thus, for example, in the0.647:1 mode, a 17-inch document is scanned in the same time as it takesthe drum to rotate a distance sufficient to lay down an image of an11-inch document. Accordingly, the 17-inch document is reduced in sizeto that of an 11-inch document. Since the velocities for the differentmodes are inversely proportional to the reduction factor, this holdstrue for any selected reduction mode in a continuous range of reductionmodes.

FIG. 6 shows trajectories whose starting times t₁ -t₅ relative to drumposition, are different for each trajectory. As mentioned above,however, preferably, the scan starting time, relative to drum position,is identical. This can be effected by lengthening the scan time durationas shown dotted in FIG. 6. Thus, the lowest velocity trajectory ratherthan starting at time t₁ (after time t₅, the starting time for thehighest velocity trajectory) also starts at time t₅. Accordingly, thecarriage reaches its constant velocity at time t₆ (rather than at thetime t₇). Thus, the constant velocity phase of movement is lengthened intime by the difference between times t₆ and t₇. By utilizing the sameprocedure, the scan start time can be identical for each mode, i.e., t₅.Using this technique, the time duration of the constant velocity phaseof motion differs for each mode although the time during which the imageis created is still identical for all modes.

As mentioned above, when not operating, the carriage is in a home orreference position. Before scanning can take place, the carriage must berescanned, since scanning takes place toward the home position. Thedistance through which the carriage is scanned (and therefore rescanned)depends on the reduction mode for reasons which will now be explained.It should be clear that the distance the carriage travels during theconstant velocity phase is related (perhaps directly) to the amount ofreduction taking place. In addition to this distance, however, thecarriage must be rescanned sufficiently far to allow for theacceleration phase of its movement during scanning. In one preferredembodiment of the invention, a common acceleration is employed for allaccelerating movements and thus the acceleration phase, in terms of timeor distance, lasts longer for those trajectories with higher constantvelocity phase. Typically, therefore, the carriage is rescanned by aunique distance which is related to the selected reduction mode in acontinuous range of reduction modes. This rescan distance may beincreased from this value to a different but also unique value if, as inone preferred embodiment, it is desired to employ a common starting timefor all trajectories. Once the carriage is properly rescanned, it isready for movement in the scanning direction but that movement must betimed properly relative to the image area on the drum so that theleading edge of the image is laid down at the leading edge of the drumimage area, e.g., see FIG. 6. The acceleration phase of the scanningmovement is controlled so as to bring the carriage up to the desiredvelocity commensurate with the selected reduction mode. During theconstant velocity phase of the motion, the carriage velocity is lockedto the drum so that the velocity ratio is constant at the desiredreduction mode. At the conclusion of the constant velocity phase of thecarriage movement, it is decelerated and stops at the home position.

FIG. 7 is a block diagram of the apparatus to control the carriagemovement in accordance with the foregoing description noted CONTROL 15in FIG. 1.

FIG. 7 illustrates the major components for producing the desiredcarriage motion as well as the components which control such motion.More particularly, the drum 13 is illustrated at the left and it isassociated with a tachometer 22. In addition, at the upper right, thelens motor 18 is shown controlling the position of the lens 9. The lensposition is sensed by a lens tachometer 21 (and 21a) which provides aninput to a processor 111. The servomotor 70a which drives the carriage60 is also illustrated associated with a carriage tachometer 23. A homeswitch H is shown which is normally open and closed when the carriage isin its home or reference position.

The major components included in the control loop include a referenceclock 104, phase detector 105, filter 106, compensation network 107,summing device 109, power amplifier 410, servomotor 70a, a tachometer23, and interface 100. During the constant velocity phase of motion, thereference clock outputs a pulse train proportional to velocity of drum13, with a proportionality factor selected by processor 111 independence on the selected reduction mode. Speed of servomotor 70a (andhence, carriage assembly 60) is sensed by tachometer 23 and coupled tophase detector 105. Velocity error signal from phase detector 105 isfiltered and compensated and coupled to the power amplifier 410 tocorrect for the speed error. At the beginning of carriage travelprocessor 111 loads a (position) counter in the interface 100 with aquantity related to desired travel length. The (position) counter isdecremented by the tachometer output; the counter contents thereforerepresent the difference between carriage position and the end point ofcarriage travel. A second counter is incremented from zero duringacceleration. Periodically, as referenced to drum motion, the processor111 is interrupted and present carriage position from the start oftravel (contained in the second counter) is compared to desired positioncontained in a table in processor memory. The difference, or error, isconverted to analog form and may be used to regulate the acceleratingsignal to maintain the carriage on the desired trajectory. At theconclusion of acceleration, the second counter is stopped. Decelerationcan be initiated when the counts in the position counter and the secondcounter compare. Deceleration can be open or closed loop. In closed loopdeceleration, the processor in interrupted and actual carriage positionis compared with desired position and an error signal is developed tocontrol the deceleration. At the conclusion of the decelerating phase ofmotion, the position counter may be used to drive the carriage to theproper position, either home or its rescanned location.

Once the carriage is in the scanning position, the initiation ofscanning is determined with reference to drum position. Since thecarriage follows constant acceleration, more time is required toaccelerate to a higher speed than to accelerate to a lower speed. Thetime taken to reach desired velocity can be expressed as K/M, where M isthe reduction mode, i.e., from 1.0 to 0.647 and K is a constant, in oneembodiment 0.035.

Before describing the detailed structure and operation of the apparatusshown in FIG. 7, an overview of the operation performed thereby ispresented.

When power is applied, processor 111 checks that the carriage is in thehome position by noting the condition of the home position switch H. Inthe stand-by mode, the carriage is maintained in this position by theinterface 100. The processor 111 determines whether or not the machineis in reduction by noting the position of the lens 9 as reflected by theaccumulated signals from the lens tachometer 21. From the position ofthe lens 9, the reduction mode is determined and a velocity scale factoris calculated. In one embodiment, carriage velocity at 1:1 was13.6"/sec., and for other reduction modes is 13.6/M. For each differentreduction mode, the carriage travels a unique distance in the scan andrescan movements, and this distance is also determined. While thedistance could be calculated, in one preferred embodiment of theinvention, a table in the processor 111 stores distance counts (of tach23) versus reduction modes and the processor determines the distance tobe travelled by a table look up. In addition, the acceleration time isalso computed, again based on the formula described above. Actually, theprocessor determines how many times it may be interrupted duringacceleration to make corrections. This is proportional to theacceleration time, at least to a first approximation. When the foregoingfunctions have been completed, the processor awaits energization of thestart button by the operator.

When that function is accomplished, the total distance to be moved bythe carriage, computed as above, is loaded into the position counter ininterface 100 in terms of a number of tachometer pulses via bus 111A. Inaddition, the appropriate velocity scale factor is loaded into thereference clock 104 via bus 111B. For rescan, the velocity used is thehighest available regardless of the reduction mode, that is, on rescanthe velocity is 13.6/M"/sec. where M is the smallest avaiable, i.e.,0.647. The processor 111 then monitors drum position via the encoder108, decoder 108a and the accelerate signal (ACCEL) is provided to thesummer 109 via unit 112, allowing the carriage to accelerate at theproper time. Encoder 108 can recognize a plurality of unique drumpositions for starting carriage acceleration, one for reduction mode,and others, in a 1:1 mode for various paper lengths. Accordingly,decoder 108a raises a line corresponding to the unique drum position forstart of acceleration in a reduction mode and the processor 111 respondsby outputting ACCEL to accelerate unit 112. The accelerate/decelerateunit 112 is merely a voltage source for summer 109. In response toACCEL, a particular voltage is provided to summer 109 which corresponds,in amplitude, to that voltage necessary to cause carriage accelerationat the selected rate of acceleration. Another voltage level, withappropriate polarity, is employed for deceleration which is produced inresponse to DECL. Finally, in response to ACCEL, DECL or constantvelocity motion, a small level is applied to summer 109 to compensatefor friction effects. At the same time, processor 111 ensures that thephase detector 105 is disabled.

Simultaneously, with ACCEL the phase detector 105 is disabled so thatduring the acceleration phase of carriage movement it plays no part incontrolling the servo motor 70a. In addition, an interrupt clock ininterface 100 is initiated, and the processor 111 is periodicallyinterrupted by the clock. The clock is derived from the drum tachometer22 in a manner to be explained.

At periodic intervals, governed by the interrupt clock, the processorreads the carriage position over carriage position bus 111A from anacceleration counter which counts tachometer pulses during theacceleration phase of motion. The processor 111 then compares actualposition with a theoretical position for the carriage. While thetheoretical position of the carriage could be computed repeatedly duringthe interrupt phase of the processor operation, in a preferredembodiment of the invention, a table is provided, entry into which isdetermined by the particular interrupt for a selected reduction mode;the table providing the theoretical or desired carriage position count.Processor 111 then computes the error (the difference between thecounts) and provides an error correction input to a digital to analogconverter within interface 100 via ERROR bus. This error, converted toanalog form and applied to summer 109 through compensation 107,maintains the carriage on the proper acceleration curve. This operationis repeated for each interrupt of the processor. On the next to lastprocessor interrupt, the phase detector 105 is enabled. On the lastprocessor interrupt, the signal ACCEL is removed. This terminatescounting by the acceleration position counter, and disables theinterrupt clock and the digital to analog converter. Enablement of thephase detector 105 completes a velocity error feedback loop to maintainthe carriage velocity at a predetermined ratio with drum velocity, theratio being determined by the scale factor loaded into the referenceclock 104. Accordingly, the carriage is now locked to the drum movement.Continued movement of the carriage continues the decrementing action ofthe position counter. When the position counter reaches the count in theacceleration position counter, the phase detector 105 is again disabledand a logic signal DECL is provided from interface 100 to processor 111.In response, the processor 111 produces DECEL. The signal DECEL, at unit112, produces a decelerating voltage to the summer 109. Accordingly, theservo motor 70a is decelerated until the carriage position counter getsto within a few counts of the desired position. At this point, theprocessor turns off the signal DECEL and the position counter is used toposition the carriage.

At this point, the carriage now is positioned for scan. In oneembodiment of the invention, deceleration is open loop. In anotherembodiment, deceleration is the mirror image of acceleration in that theacceleration position count may be compared to desired position and anerror signal generated to maintain deceleration on the desired profile.

The processor 111 initiates the scanning movement again based on drumposition as reflected by the position encoder 108. Prior to initiatingscanning movement, however, the processor again sets the carriageposition count for the desired movement back to the home position andnow the reference clock 104 is loaded with a scale factor dependent uponthe reduction mode. At the proper time, the signal ACCEL is againprovided and the phase detector 105 is disabled. The interrupt clockbegins again and the processor is continually interrupted, at periodicintervals, to compare actual carriage position with desired position andmake the appropriate corrections. Several interrupts before the last(two, for example), the phase detector 105 is enabled, on a followinginterrupt, the signal ACCEL is removed and on the last interrupt, thedigital to analog converter and the interrupt clock are disabled. Thecarriage is now locked to the drum movement through the velocity errorloop at the desired velocity. During this movement, the position counteris continually decremented, and when the signal DECEL is provided muchas in rescan, the phase detector 105 is disabled, and the carriagedecelerates until the position counter comes within a predeterminedrange of the home position. At this point, the processor 111 removes thesignal DECEL and the position count is used to stop the carriage at oradjacent the home position.

The apparatus to perform these functions is shown in FIG. 7 and includesthree mechanical systems, inter-related to produce the desired effects.Firstly, the drum 13, which is driven open loop by the main AC motor 10,is used as a speed reference in the constant velocity phase of thecarriage travel. The proportionality factor is determined by theselected reduction mode, and in order to determine what reduction hasbeen selected, the position of lens 9 is monitored. Changes in positionof the lens 9 produce tachometer signals on the tachometer 21 which areused to increment or decrement a register in the processor 111;accordingly, the register in processor 111 maintains a quantity relatedto the position of the lens 9 from which the reduction mode can bedetermined. Motion of the carriage itself is detected by a tachometer23, and, during the constant velocity phase of motion, is fed back tothe phase detector 105. Thus, one servo loop, in analog form,encompasses the reference clock 104, phase detector 105, filter 106,compensation network 107, power amp 410 and the motor 70a with thefeedback path corresponding to tachometer signals input to the phasedetector 105. (The summer 109 is used only to compensate for frictionsince the only other input during constant velocity phase of motion isthe friction compensation level.)

In the acceleration or deceleration phases of movement, the phasedetector 105 is disabled and a different feedback path may be employed.More particularly, the accelerate/decelerate signal from unit 112 iscoupled as an input to the summer 109 which energizes the motor 70a todrive the carriage. Carriage position is monitored by the interface 100which interrupts the processor 111 for a comparison. Any errors as notedby the processor are coupled through the ERROR bus, converted to analogform and coupled as an input to the compensation network 107 to enablethe summer 109 to form an error signal which is the difference betweenits inputs. Accordingly, the preceding apparatus corresponds to a secondfeedback loop. As mentioned, the second feedback loop may be used onlyfor acceleration purposes, or it can also be used during decelerationphases of motion as well.

Finally, there is still another feedback loop which is used to actuallystop the carriage either at its home or start of scan position. In thisloop, which is only enabled at the termination of the deceleration phaseof motion, differences between the carriage position and desiredposition (zero or near zero count) are converted to analog form and areemployed as a driving signal to drive that position error to zero.

Accordingly, the interface 100 and processor 111 exchange a plurality ofsignals therebetween. Initially, the extent of carriage positionmovement is transferred from the processor 111 over the carriageposition bus 111a to the interface 100 where it is used to preset acounter (position) which will be decremented by the output of thecarriage tachometer 23. In addition, the processor raises the scan orrescan signal to indicate what type of movement is to occur and may alsoraise ACCEL or DECEL at the appropriate times. Actually, thedeceleration phase is initiated by the interface 100 in raising thesignal DECL to the processor 111. In addition, the interface 100provides the interrupt signal during acceleration and decelerationphases to enable the processor to make a comparison. Carriage positionis transferred to the processor over the carriage position bus 111a forcomparison purposes. Position error in acceleration and perhaps indeceleration phases is coupled back to the interface 100 over the ERRORbus where it forms an input to the digital-to-analog converter, DAC.

Further inputs to the processor 111 include the machine mode and status.For example, whether or not the operator has selected a reduction, andwhether the machine is in stand-by or the start button has been pushed.Finally, the initiation of carriage motion is tied to unique positionsof the drum 13. To detect drum position, a position encoder 108 rotateswith the drum and a decoder 108a monitors the signals provided by theencoder. There may be, for example, unique drum position at which it isdesired to start the rescanning and scanning movements in the reductionmode, and still other drum positions may be used for 1:1 mode withvarious paper lengths. Accordingly, the decoded drum position is coupledto the processor 111 over the reference bus.

FIG. 8 illustrates the components included in the interface 100. Thecarriage position counter is actually duplicated, and thereforecomprises a pair of counters. In the embodiment shown in FIG. 8, eachcounter comprises serially connected pair of up/down counters. Thus, afirst counter comprises counters 201, and 202, and the second countercomprises counters 203 and 204. These counters may be preset, in commonfrom the carriage position bus 111a by the processor 111. Although thecounters normally count down only, if the carriage overshoots itsintended position, up counting may be necessary and this function isaccomplished by logically gating signals from the tachometer 23 with theSCAN signal from the processor in the exclusive NOR gates 205, 206 andNAND gates 207, 208. Since scan and rescan states are mutuallyexclusive, a single signal will suffice.

A further counter is the acceleration position counter which againcomprises a pair of serially connected up/down counters 209, 210. Thiscounter counts up during acceleration, and down during deceleration.This up/down control is accomplished by gating the ACCEL and DECELsignals from the processor 111 with signals from the carriage tachometer23 in a pair of NAND gates 211 and 212. The processor also provides areset signal for counters 209, 210 to insure that the accelerationposition counter starts counting from its zero state. Outputs of theacceleration position counter are coupled to the carriage position bus111a from which their count is available at the processor 111 forpurposes of comparison. In addition, the counter outputs are coupled toa comparator 213 where their count is compared to the carriage positioncount contained in the counters 203, 204. This comparison, as will beexplained hereinafter, is employed to initiate the DECL signal which isalso coupled to the processor 111. The outputs of the counters 203, 204are also coupled to a further comparator 214 where the count is comparedagainst zero, and when zeroed, the output is employed to disable theDECEL signal from the processor.

The interrupt clock to the processor is provided by a further counter215. Inputs to this counter are generated by an OR gate 216 and a NANDgate 217. Inputs to OR gate 216 are the ACCEL and DECEL signals, fromthe processor. The input to NAND gate 217 is the output of OR gate 216and a signal from the drum tachometer 22. Accordingly, when in eitherthe accelerate or decelerate phase of motion, counter 215 is enabled tocount; it will count a specified number of drum tachometer pulses beforeproducing the interrupt output to the processor and reset itself.Accordingly, the processor is interrupted at equally spaced incrementsof drum travel.

At the conclusion of deceleration, the carriage has travelled thedistance originally loaded into the counters 201, 202. However, sincethe position of the image which is laid down on the drum is determinedby the travel of the carriage, an attempt has been made to avoid orminimize position errors. This is especially true at the conclusion ofthe rescanning movement since the location of the carriage at that timewill be its starting position for the scanning movement. Accordingly,the output of the counters 201, 202 is monitored through a gatingnetwork 218, when enabled by the latch 219. Thus, when the gatingnetwork 218 is enabled, the condition of the counter 201, 202 is coupledvia a plurality of exclusive OR gates 219 to a buffer 220. The buffer220 provides an input to the digital to analog converter 221, whoseoutput is the input to the compensation network 107, in the servo loopfor the motor 70a. Thus, position error of the carriage produces adriving signal to energize the motor. Assuming that the carriage had nottravelled the length desired, the counters 201, 202 contain a positivecount and thus, the resulting voltage output of the digital to analogconverter causes the motor to move the carriage in the direction oforiginal motion. If, however, the carriage has overshot its desiredposition, or if succeeding motion causes the carriage to overshoot itsdesired position, the counters 201, 202 will count through zero and, asis well known to those skilled in the art, the immediately succeedingcount will be a very high, albeit negative, number. However, the borrowline 222 will also go high, resetting a flip-flop 223 and raising thecomplement signal which forms the other input to the exclusive OR gate219. This will cause the output of the digital to analog converter 221to change sign which will result in reversal in the motor direction.This will be reflected by causing the counter now to count up, ratherthan down, by reason of the gates 205-208. Accordingly, the loopmaintains an unambiguous reference at the zero point and drives thecarriage to it, regardless of overshoots.

Since carriage motion also changes in direction between the rescan andscan motions, a latch 224 responds to appropriate signals from theprocessor to control the sign of the output of the digital to analogconverter to maintain the carriage moving in the proper direction.Similarly, the SCAN signal from the processor is coupled as one input toone of the exclusive NOR gates 205, and this signal negatived byinverter 225 is the other input to the other exclusive NOR gate 206. Asa result, as the carriage travels during the rescan operation, thecounter is counting down. If the carriage stops before the counter hascounted to zero, the remaining count in the counters 201, 202 produce anoutput voltage at the output of the digital to analog converter 221 ofsuch a polarity to drive the carriage in the direction in which it hadbeen travelling prior to stopping. If, however, the carriage passes theintended stopping point, the counter counts through zero and beginscounting in effect, negative numbers. This would ordinarily result in arelatively high voltage, but this effect is prevented by thecomplementing action directed by flip-flop 223. The resulting voltagewill drive the carriage in its opposite direction because of the signchange at the input to the DAC. The change in direction of carriagemotion will be reflected in the tachometer output and accordingly, thecounter will now count up, i.e., back towards zero. When the carriagehas finally been properly positioned, the processor drops the RESCANsignal and raises the SCAN signal and again loads the counters 201, 202.When the carriage begins moving in its scan direction, i.e., opposite tothe rescan direction, the counter still counts down since both the SCANsignal and the tachometer output are changed in polarity. At theconclusion of the scan motion, terminal operations are similar to theterminal operation of the rescan movement, i.e., if a carriage stopsshort of its intended stopping point, the low voltage out of the DACwill drive the carriage in the same direction in which it had beentravelling, i.e., toward the stopping point, the sign change resultingfrom the counter counting through zero will cause the motor to reversedirection and drive the carriage toward its stopping point.

FIGS. 9A through 9C illustrate the operations carried out in theprocessor 111 in order to produce the necessary signals. The processordetermines whether the ACCEL or DECEL signals are up or the phasedetector is enabled. If neither of the signals are up and the phasedetector is disabled, then the machine is truly in stand-by. At function301, the processor determines the mode, which is a function of operatorinputs; if in the reduction mode, the processor, at function 302, readsthe lens position. As mentioned, the processor maintains a register inwhich lens position tachometer signals are integrated and thus,maintains a count corresponding to lens position. This count is directlyrelated to the reduction mode M. Function 303 calculates, from thereduction mode, the velocity scale factor 1/M. In an embodiment of theinvention in which constant velocity carriage travel is at 13.6 inchesper second for 1:1 mode, the velocity in reduction is merely 13.6/M.When calculated, this quantity is stored in a register TEMP 1. Function304 extracts carriage count and loads it into a further register TEMP 2.As mentioned previously, the processor maintains a table of carriagetachometer pulses versus reduction mode and thus function 304 merelyrequires reference to the table. If desired, the processor can beprovided with a simple routine to interpolate if the selected reductionmode lies between entries in the table. On the other hand, this is notessential to the invention and function 304 could determine the closesttable entry for the selected reduction mode and employ that count.Function 305 extracts the number of acceleration corrections orinterrupts that are expected. This function is implemented employing atable similar to the table referred to with respect to function 304, andsimilar considerations respecting interpolation between table entriesapply. Function 306 determines if the start button has been pressed. Ifit has not, the routine loops back and reperforms these functions untilthe start button depression is detected. When that occurs, function 307outputs the carriage count from the register TEMP 2 and clears the same.The carriage count is placed on the carriage position bus and, as shownin FIG. 8 serves to load the pairs of counters with the identical count.Function 308 selects the maximum velocity scale factor and places thatquantity on the velocity scale factor bus where it is loaded in thereference clock 104 (see FIG. 7). This implements the use of maximumvelocity in the rescan operation, as mentioned. Function 309 resets theacceleration position counter by raising the signal RESET coupled to theresetting inputs of counters 209, 210 (FIG. 8). Function 310 refers tostill another table to select the drum position for the start ofacceleration signal and stores the same in a register TEMP 4. Asmentioned, in a preferred embodiment of the invention, the start ofacceleration is identical for all reduction modes, but the start ofacceleration may vary for 1:1 mode operation depending upon the size ofcopy paper being employed. In any event, this value which corresponds toa unique drum position is loaded into the selected register. Function311 compares the present drum position with the quantity in the registerTEMP 4. Present drum position is reflected on the drum reference busfrom decoder 108a. When the drum reaches the selected position, function312 outputs RESCAN and ACCEL signals and clears the register TEMP 4.Function 313 disables the phase detector and the processor returns tostand-by since, once having launched the carriage by enabling the RESCANand ACCEL signals, further control is on an interrupt basis.

FIGS. 9B and 9C illustrate the interrupt routine. As shown, when aninterrupt is detected, function 314 determines if the ACCEL signal isup. If it is, then function 315 decrements the register TEMP 3, which isthe register in which the number of corrections has been stored.Function 316 determines if that register has been decremented to zero.Assuming it has not, function 317 reads the carriage position. Duringthe acceleration phase, carriage position is reflected in theacceleration position counter 209, 210 which signals are available atthe processor over the carriage position bus. Carriage position isstored at a register TEMP 2. Function 320 reads the desired carriageposition and loads that value into register TEMP 5. The value read isdetermined by the mode M and the particular interrupt which is the valuestored at the present time in TEMP 3. Function 321 produces thedifference, loads the same in TEMP 2 and clears TEMP 5. The differenceis the error between desired carriage position and actual carriageposition. Function 322 outputs that error on the ERROR bus where it isprovided as an input to buffer 220 (see FIG. 7B). Function 323determines if the value in TEMP 3 has been decremented to 2. Assuming itis not, function 324 determines if the quantity has been decremented toone. Again, assuming it has not, the routine is concluded untilreception of the next interrupt.

This routine will be operated a number of times in a similar fashion,each iteration producing an error signal if there is a differencebetween present carriage position and desired carriage position whicherror is employed to maintain the carriage on the desired accelerationtrajectory. When the quantity in the register TEMP 3 has beendecremented to two, function 325, following function 323, will enablethe phase detector 105 (see FIG. 7). As a result, a velocity errorsignal will begin to be produced. On the next iteration of the interruptroutine, function 326 following function 324 will disable the signalACCEL. Finally, on the next iteration, the routine will note that TEMP 3has been decremented to zero, and accordingly, function 327 will disableDAC 221.

The carriage now enters the constant velocity phase of motion which iscontrolled by the analog servo loop. Since the ACCEL signal has beendisabled, counters 209, 210 are no longer capable of counting andtherefore, they maintain a quantity corresponding to the number ofcarriage tachometer pulses produced during the acceleration phase ofmotion. However, the carriage position counters 201 through 204 continuedecrementing throughout the constant velocity phase of motion. Adiscussion of operation of the analog servo loop will be postponed untila discussion of FIG. 10 which illustrates the reference clock 104 indetail. Suffice it to say, however, that the carriage velocity ismaintained in a preselected relation to that of the drum 13.

The deceleration phase of carriage movement is initiated by comparingthe static count in the counters 209, 210 with the continuallydecremented count in the counters 203, 204. Thus, when the remainingtravel distance for the carriage is equal to the distance travelledduring the acceleration phase, these counts are equal, and comparator213 issues the DECL signal to the processor. In turn, the processorraises the DECEL signal. This signal is one input to NAND gate 212,which then allows the counters 209, 210 to begin counting down. Inaddition, the same signal is an input to OR gate 216 which allowscounter 215 to count and to periodically produce interrupt clock to theprocessor.

Production of the DECL signal by comparator 213 results in applying avoltage to the summer 109 for the purpose of decelerating the carriage.In addition, phase detector 105 is disabled.

In one embodiment of the invention in which deceleration is accomplishedopen loop, no error signal is developed in the feedback path. In apreferred embodiment of the invention, however, the processor respondsto the interrupt clock and compares carriage position from its intendedstopping point to a theoretically desired position, and develops anerror signal to maintain the carriage on the desired decelerationtrajectory.

When the processor receives the first interrupt, from counter 215, inthe interrupt routine function 314 determines that the DECEL signal isup, signifying the deceleration phase of motion. Function 329 decrementsthe register TEMP 6, which has been loaded (at function 305--FIG. 9A)with a number of corrections or interrupts in the acceleration ordeceleration phase of motion. Function 330 checks whether the quantitycontained in this register is equal to zero. Assuming it is not,function 331 reads the present carriage position from the carriageposition bus and stores the quantity at TEMP 2. During decelerationphase of operation, the acceleration position counter 209, 210 containsa count corresponding to the present number of tachometer pulses betweenthe carriage's present position and its intended stopping point.Accordingly, this is the count corresponding to the carriage positionread at function 331.

Function 332 reads the desired position from a table. The desiredposition is contained in a table entered from the reduction mode M andat an entry corresponding to the present value contained in the registerTEMP 6. Function 333 determines the difference therebetween, stores itat TEMP 2 and clears TEMP 5. Function 334 outputs the value in TEMP 2,i.e., the error, on the ERROR bus, and that concludes the particulariteration of the interrupt routine.

On succeeding passes of the error routine, similar operations occur. Atthe conclusion of the intended number of passes, the register TEMP 6will have been decremented to zero, concluding the deceleration phase ofoperations.

The interface 100 also includes an additional comparator 214 whichcontinually compares the quantity contained in counters 203, 204 to apredetermined reference quantity, such as zero. When the count in thecounters 203, 204 reaches zero, the carriage has travelled its intendeddistance, and the output of the comparator coupled to the processor,disables the DECEL signal, thus removing the potential from summer 109.The same signal coupled to latch 219 enables the gating network 218.

Because of friction effects, which cannot be exactly predicted, as wellas aging of component parts, etc., the actual zero point, or the pointat which the deceleration signal is removed is in a range of valuesaround the desired stopping point. Accordingly, that is the value usedas a reference in comparator 214. At the same time, the carriage maystop short of its intended stopping point, or it actually may overshootthe stopping point. In either event, the counters 201, 202 will maintaina count corresponding to the carriage's position, and enablement of thedating network 218 allows that count to be coupled through exclusive ORgates 219 to a buffer 220. As has been mentioned above, the count may becomplemented under control of the flip-flop 223 in the event that thecarriage passes through the zero point. The buffer 220 enables thisdigital count to be made available to the digital to analog converter221, wherein it is converted to an analog quantity which is applied tothe compensation network 107 to allow it to energize the servo motor todrive the carriage toward its intended stopping point or zero position.Those skilled in the art will recognize that the driving voltage for theservo will only be reduced to zero when the count in the counters 201,202 is reduced to zero. Accordingly, a further, or third, servo loopencompasses the output of the digital analog converter through thecompensation network 107, summer 109, amplifier 410, a servo 70a, afeedback path through the tachometer to the gates 205-208, the counter201, 202, gating network 218, exclusive OR gates 219 and buffer 220,back to the digital to analog converter 221.

The preceding discussion has described the rescan motion of thecarriage, i.e., from its start or home position to its start of scanposition. As has also been described, the particular count or distancethrough which the carriage travels depends upon the reduction modeselected by the operator if the machine is in the reduction mode. At theconclusion of rescan operation, i.e., when the carriage is properlypositioned at the desired location, the scan operation may commence todrive the carriage back toward its home position and, during this pass,to transfer an image from the document to the image carrier. The scanmotion includes acceleration, constant velocity, and decelerationphases. The operation is identical to the rescan save for the particularvelocity scale factor used. In rescan, the maximum velocity scale factoris used whereas during scan, the computed velocity scale factor,computed in relation to the desired reduction mode, is employed.

The preceeding discussion describes, in detail, the acceleration,deceleration and stopping modes of operation. Constant velocity phase ofmotion will now be described.

The block diagram of FIG. 7 shows the analog control loop employedduring the constant velocity phase of motion. As mentioned above, thephase detector 105 is selectively enabled or disabled as the carriagetravels through its various phases of motion. As the acceleration phaseterminates, the carriage has been brought up to the proper velocity, andthe phase detector 105 is enabled. Desired velocity for the carriage isproportional to image carrier velocity, i.e., the drum 13, with aselected proportionality factor selected in dependence upon thereduction mode M. The drum velocity is detected by the tachometer 22which produces, as an input to reference clock 104, a train of pulseswhose rate is related to the velocity of the drum 13. A further input tothe reference clock 104 is the velocity scale factor from the velocityscale factor bus 111b. The output of the reference clock 104 is a pulsetrain whose rate is proportional to the input pulse train, by theproportionality factor transmitted on the velocity scale factor bus111b. The other input to the phase detector 105 is a further pulse trainfrom the carriage tachometer 23, whose rate is related to actualcarriage velocity. The output of the phase detector 105 is a pulse trainin which the pulse widths are related to the difference in the rates ofthe incoming pulses, i.e., the velocity error, and whose polaritydepends upon whether or not the actual carriage velocity is greater thanor less than the desired carriage velocity. The signal is low passfiltered in filter 106, passed through the compensation network 107 andapplied as an error voltage to summer 109. The accelerate, deceleratemodule 112 which, during the acceleration or deceleration phases,applies a selected potential to the summer 109 to accelerate ordecelerate the motor 70a, in the constant velocity phase, applies a muchlower potential designed to overcome frictional effects. The algebraicsum of these potentials are employed as an input to the power amp 410 toenergize the servo motor 70a, to maintain its velocity constant at thedesired value. FIG. 10 illustrates the components in the reference clock104.

As shown in FIG. 10, the output of the tachometer 22 is applied to aphase detector 130. The output of the phase detector 130 is a voltagelevel which is input t a voltage frequency controlled oscillator 131.The output of the voltage frequency oscillator is coupled to a divider132 to provide an appropriate scale factor. The output of the divider132 is coupled as the other input to the phase detector 130. The VFO 131thus outputs a pulse train which is related in repetition rate to theoutput of the tachometer 22, by the proportionality factor N. This pulsetrain is input to a counter 133. Counter 133 is preset by the velocityscale factor bus 111b. The counter 133 produces an output each time itreaches its terminal count which clocks flip-flop 134 and also serves toallow the counter to be again preset to the quantity contained on thevelocity scale factor bus. As will be apparent to those of ordinaryskill in the art, the repetition rate at which the flip-flop is clockedis determined by the repetition rate of the output of the VFO 131 aswell as the quantity to which the counter 133 is preset. The output ofthe flip-flop 134 is thus a pulse train with repetition rate which isrelated to these two quantities and which may be compared with the pulsetrain output of the carriage tachometer 23 to develop a velocity errorsignal.

A Second Preferred Embodiment

The preceding portion of the detailed description of a preferredembodiment has described a first preferred embodiment of the inventionwhich employs multiple, overlapping servo loops to control,respectively, acceleration and deceleration, constant velocity, andstopping modes of operation of the scanning carriage assembly. Inanother preferred embodiment of the invention to be disclosedimmediately hereinafter, only a single servo loop is employed to controlthe servo motor during acceleration, constant velocity, deceleration andstopping phases of motion.

The single control loop is similar to the control loop employed in thefirst preferred embodiment for constant velocity motion in thatapparatus similar to the phase detector 105 is employed to compare adriving signal pulse train wherein each pulse represents a desiredincrement of motor travel, with a tachometer pulse train representativeof actual travel, the difference therebetween utilized as an errorsignal to drive the motor. In the first preferred embodiment, thedriving signal pulse train is produced in a counter which is clocked ata rate determined by the velocity of the image carrier, the pulse in thedriving pulse train is produced each time the counter reaches apredetermined count, such as the terminal count, and in order to producethe driving pulse train of various repetition rates, so as to providefor various velocities of the scanning carriage assembly, the counter ispreset each time it reaches the predetermined count, and the quantity towhich it is preset, of course, is instrumental in determining therepetition rate of the driving pulse train. The second embodimentemploys a similar arrangement except that acceleration and decelerationmovements are also produced in the same control loop so as to eliminatethe necessity for a different or further acceleration/decelerationcontrol loop. This is simply implemented in practice by presetting thecounter to different quantities during the course of carriage movementso as to produce acceleration, constant velocity motion anddeceleration.

However, in contrast to the constant velocity control loop in the firstembodiment, the apparatus corresponding to the phase detector consistsof an up/down counter which enables the control loop not only to providean appropriate error signal for errors corresponding to less than adriving or tach pulse, but to also maintain accurate tracking for errorsactually comprising multiple driving or tach pulses. Accordingly, then,the single control loop produces a clocking signal which is synchronizedto the image carrier velocity, for clocking a counter which isselectively preset in a predetermined pattern to produce the drivingpulse signal which comprises a pulse train of variable repetition ratewhich is, itself, coupled to an input of the up/down counter, the otherinput to which is provided by the tachometer pulses. The up/down countermay count up (for rescan, for example) in response to driving signalpulses, and count up or down in response to the tachometer pulsesdepending upon the relation between the desired direction of motortravel and the actual direction of motor travel. For scan, the up downcounter may count down in response to driving pulses and the tach pulsesproduce up or down counts depending on the direction relation. The realtime contents of the up/down counter are converted to analog form andemployed as the error signal to drive the servo motor.

In contrast to the first preferred embodiment of the invention, whereina position counter is employed which is set at the beginning of a rescanmovement to a quantity related to the desired travel of the carriageduring the rescanning, and which is reset at the termination of therescanning movement and prior to the scanning movement, the singlecontrol loop of the second embodiment eliminates the position counterentirely, and the contents of the up/down counter maintain a continuousrunning count of the "error", that is, the deviation between the numberof driving pulses as compared to the number of tachometer pulses,throughout an entire cycle of scan and rescan movements, therebyeliminating any position error caused by resetting of the positioncounter at the termination of the rescan and prior to scan, and assuringthat the position profile of the carriage will be repeatable from onerescan-scan cycle to the next. Likewise, since the driving signal sourceis timed only by the velocity of the image carrier, the velocity profileof the scanning carriage relative to the image carrier is alsorepeatable from one rescan-scan cycle to the next, to within a toleranceof less than a single tachometer pulse.

FIG. 11 is a block diagram of the second preferred embodiment of theinvention, which illustrates the apparatus employed in the secondembodiment in lieu of that shown in FIG. 7. Similar to FIG. 7, inputsignals are coupled to the control loop from the drum (or image carrier)tachometer 22 as well as the scanning carriage assembly tachometer 23,and the control loop generates a signal to control the servo motor 70awhich drives the scanning carriage assembly. In contrast to FIG. 7,however, the microprocessor 100' is now no longer in the control loop.Rather, the control loop includes an up/down counter 406 which may becounted in one direction, for example, up, in response to a drivingsignal comprising a train of pulses, from a counter 403 coupled throughthe sign and count logic 405. Similarly, the up/down counter 406 can becounted down by the output of the scanning carriage assembly tachometer23 which output is coupled through the same sign and count logic 405.Each pulse output of the counter 403 represents a desired increment ofscanning carriage assembly travel, and likewise, the tachometer 23produces a train of pulses, each pulse represents a similar increment ofactual scanning carriage assembly travel. Accordingly, the up/downcounter 406 may contain a real time count of the difference between thedesired scanning carriage assembly travel and actual scanning carriageassembly travel, or a position error. In the control loop the output ofthe up/down counter 406 is coupled to drive the servo motor 70a throughthe digital to analog converter 407, and filter and compensation network408 and power amplifier 410. A friction compensation signal can also beprovided through the power amplifier 410 by a friction compensationnetwork 409, which is enabled from the sign and count logic 405.

The control loop described above operates in a manner very similar tothe operation of the first preferred embodiment during constant velocitymotion with a very significant exception. The control loop, operativeduring constant velocity motion in the first preferred embodiment of theinvention, employed a phase detector which is enabled to output an errorsignal representing the difference between the desired and actualscanning carriage velocity. The phase detector actually determined thedifference in arrival time at the phase detector 105 of a pulse from thereference clock 104 and a pulse from the tachometer 23. Undercircumstances wherein the actual and desired velocity of the carriageare substantially equal, this arrangement is effective in maintainingactual velocity at or near the desired velocity. However, since thiscircuitry is incapable of keepng track of more than one pulse positionerror it has been modified as shown in FIG. 11 to incorporate theup/down counter 406 which is capable of keeping track of position errorsgreater than a single driving or tachometer pulse. Those skilled in theart will understand that as the position error increases, the drivingsignal to the servo motor 70a likewise increases, and this can beemployed to accelerate or conversely, decelerate the servo motor 70a ina manner now to be explained.

The driving signal for counting the up/down counter 406, in a particulardirection, for example up, is derived from the output of a counter 403,which corresponds to the operation of the counter 133 (FIG. 10) of afirst preferred embodiment during constant velocity motion. That is,more particularly, the counter is cycled by a pulse train derived from aclock 401 which is synchronized to the motion of the image carrier ordrum. The counter 403 can be preset so that it counts from its presetposition to a terminal count, produces an output pulse corresponding toone pulse in the driving pulse train, and is again preset to repeat theoperation. It should be apparent that the quantity to which the counter403 is preset (assuming that the clock signal 401 is relatively stable)determines the repetition rate of the counter output, which is thedriving pulse train. In fact, by providing a sequence of quantities towhich the counter is preset in a predetermined order, the repetitionrate of the driving pulse train can be controlled. By varying therepetition rate of the output of the counter 403, the velocity profileto which the scanning carriage is controlled can be selected. Not onlycan constant velocity motion be controlled in this fashion, butacceleration and deceleration as well. Since the counter is cycled bythe output of clock 401, which is synchronized to the motion of theimage carrier, the entire control loop is maintained in step with theimage carrier velocity which is, of course, a prime requirement for themotion of the scanning carriage assembly in the copier.

The quantities to which the counter 403 is preset are derived from thelatches 404 which in turn derive these quantities from themicroprocessor 100'. Since the latches 404 buffer the operation ofmicroprocessor 100', any impediment to accurate control provided by thepoor timing of the microprocessor 100' is eliminated.

From the preceding brief discussion, operation of the second preferredembodiment should be apparent. More particularly, after the operator haspositioned the lens 9 to a desired position corresponding to a desiredreduction ratio, and enabled copying to proceed by pressing the startbutton, for example, microprocessor 100' performs the functions ofinitializing the control loop by loading the latches 404 with an initialquantity or quantities and provides a start signal to the clock 401. Atthe proper time, as determined by the position of the drum, and insynchronism therewith, the clock 401 begins producing clock pulses tocycle the counter 403. As the counter 403 reaches a terminal count andproduces an output pulse, it is again preset and continues counting.This output of the counter 403 places an intitial count into the counter406. Depending on the gain of the control loop, one or more counts maybe placed in the counter 406 before the servo motor actually beginsmoving and as it begins moving, the up/down counter responds to theoutputs of the tachometer 23. At regular intervals, timed from the clock401 which is synchronized to the image carrier or drum, themicroprocessor 100' is interrupted and new quantities are loaded intothe latches 404 for use in presetting the counter 403, and in thisfashion, the repetition rate of the output of the counter 403 can bevaried so as to require the servo motor 70a and the scanning carriageassembly to follow a desired position and velocity profile. In thisfashion, the scanning carriage assembly undergoes acceleration, constantvelocity motion and deceleration. At the termination of thedeceleration, the rescan movement is completed; in contrast to the firstpreferred embodiment, the up/down counter 406 is not reset, andaccordingly, even if there is some position error at the termination ofthe rescan movement, it will be maintained as the direction of motion ofthe scanning carriage assembly is reversed to begin the scanningmovement. The scanning movement also includes similar phases such asacceleration, constant velocity and deceleration motion. Since theup/down counter 406 is not reset, and since the only variable in theentire operation is the velocity of the image carrier, the scanningcarriage assembly comes up to its desired constant velocity at a time,in relation to position of the image carrier which is accurate to lessthan a tachometer pulse, and in one embodiment of the invention whichhas been constructed, this was less than 0.25 mm.

FIG. 12A illustrates the clock 401, and FIG. 12B illustrates some of thewaveforms produced thereby. The basic timing of this clock is producedby the VCO 412 which is driven by phase detector 411 from a pair ofinputs, one of which is provided by the drum tach 22, and the other ofwhich is a divided replica of the output of the VCO itself, thus forminga phase locked loop. Accordingly, the repetition rate of the output ofVCO 412 follows the velocity of the drum, an in an embodiment of theinvention which has been constructed, the VCO 412 output is in thevicinity of 2.3 MHz. The output of the VCO 412 is provided to a clockcircuit 413 which provides a pair of pulse trains from the output of theVCO, as shown in FIG. 12B, a first pulse train CL1 and a second pulsetrain CL2, by directing successive VCO output pulses to differentoutputs. The pulse train CL2 is employed to up count a counter 414,whose terminal count output is provided as the other input to the phasedetector 411. A decoder 415 monitors the condition of several stages ofthe counter 414 and upon recognizing a predetermined count, is latchedto produce a distinctive output signal to an AND gate 416, whose otherinputs comprise the microprocessor start signal and the unique emitterposition corresponding to the drum position at which operation of thecontrol system should be enabled. The output of the AND gate 416, thesignal ENABLE, is employed in one instance to enable a counter 417,which counts in response to the condition of a selected stage of thecounter 414. A selected stage of the counter 417, which may, forexample, be the terminal count, provides an interrupt signal to themicroprocessor. The number of stages in the counter 414 and 417 areselected so that, at the nominal drum velocity, the microprocessor isinterrupted often enough to load the latches 404 as required for properoperation. In the embodiment of the invention which has beenconstructed, this interrupt rate was approximately once every 3.4milliseconds.

It should be apparent from the foregoing that the operation of thecontrol loop is initialized to begin operations at a predeterminedposition of the image carrier since the operations of the control loopitself do not begin until the ENABLE signal is produced, as will bespecified hereinafter.

FIG. 13 illustrates the counter 403, the latches 404 which load it, andthe load logic which controls the loading of the latches 404 and thecounter 403, and the gate which enables the counter 403 to count. Moreparticularly, the latches include latches 404a, 404b and 404c. Latches404a, and 404b are coupled to the microprocessor data bus, and theoutputs of latches 404a and 404b provide the input to latch 404c. Aplurality of the stages of latch 404c provide a setting input to acounter 403 to change the modulus of that counter in accordance with thequantities stored in the plurality of stages of the latch 404c. AND gate424 provides an output to the down counting input of the counter 403,the input to the gate 424 comprising the CL1 signal and the ENABLEsignal. Accordingly, when the ENABLE signal is produced, the gate 424provides the CL1 pulses to the counter 403 to enable it to count down.

Thus, the counter 403 counts down from a state, either reset state orthe state to which it is set by latch 404c. The output pulse, fordriving the servo motor, is produced by an underflow. The repetitionrate of the underflow pulse is controlled by selecting the quantity towhich the counter is set. Completely equivalent would be using anoverflow to drive the servo motor, in which case counter 403 is countedup from an initial set state. Similar effects are achieved by using acomparator, one input of which is the latch 404c and another input ofwhich is the condition of counter 403 and producing a driving pulse onan equal comparison and resetting the counter. In either of these threearrangements, the modulus of the counter and therefore the repetitionrate is determined by the latch 404c.

The load logic 402 includes the decoders 420, 421 and OR gate 423. Asshown in FIG. 13, the microprocessor address bus forms one input todecoder 420, another input of which comprises the microprocessorread/write line, and the third input is the signal CL1. On decoding aread at an appropriate address, the signal LOAD A is produced andcoupled to latch 404a which then accepts the information existingsimultaneously in the microprocessor data bus. Accordingly, at CL1 (whenthe microprocessor has addressed an appropriate memory area) latch 404ais loaded; in similar fashion, but based upon a different address, at adifferent CL1 time, the signal LOAD B is produced to enable latch 404bto be loaded by the data on the microprocessor data bus.

The load logic 402 also includes decoder 421, one of whose inputs is themicroprocessor address bus, a second of whose inputs comprises amicroprocessor read/write signal, and a third input comprises theclocking signal CL1. The foregoing inputs are employed during systeminitialization or start-up to provide the LOAD C signal through the ORgate 423 to load latch 404c from the contents of latches 404a and 404b.At other times, the LOAD C signal is produced in response to theINTERRUPT signal also coupled through the OR gate 423; the INTERRUPTsignal is produced by the counter 417 (see FIG. 12A). Accordingly, atall times other than start-up, latch 404c is loaded and the rate atwhich it is loaded depends upon counter 417 which is, of course,synchronized to the image carrier velocity.

Finally, the load logic 402 includes AND gate 422 whose inputs comprisethe clocking signal CL1 and the COUNT signal produced when the counter403 produces a borrow. Accordingly, at that time, the counter 403 isloaded with the contents of a plurality of stages of the latch 404c.

Finally counter 403 also counts a count down signal produced by an ANDgate 424, whose inputs are the signal ENABLE and the clocking signalCL1. The former signal is produced by the gate 416 (see FIG. 12A).Accordingly, it should be apparent that the counter is loaded on thefirst available CL1 signal after the latch 404c has been loaded by thelatches 404a and b, and it begins counting down with the first CL1signal existing after the signal ENABLE is produced.

Since the clocking signal CL1 is produced in synchronism with thevelocity of the image carrier, the counter 403 is counted down at acorresponding rate. In the absence of a setting input to the counter 403from the latch 404c, the counter 403 produces a COUNT signal at a ratedetermined by the capacity of the counter 403 and the rate at which theCL1 signal is produced. That rate, however, can be decreased by settingthe counter 403 initially to the quantity from the latch 404c. In thisfashion, the rate at which the COUNT signals are produced can becontrolled.

FIG. 14 comprises a schematic of the sign and count logic 405 and thebias up or down logic 425. The sign and count logic 405 includes a pairof gates 430 and 431, the first providing a COUNT UP pulse train and thesecond providing a COUNT DOWN pulse train, derived from the COUNT signaland differentiated with respect to whether or not the up/down counter406 is to count up or down with respect to the particular COUNT pulse.Inputs to the gates 430 and 431 comprise the signal COUNT from thecounter 403 (FIG. 11) and the signal SIGN derived from one stage of thelatch 404c and coupled directly to the gate 430 and coupled to gate 431through an inverter 432. The third input to the gate 430 and 431 is thesignal ENABLE. Accordingly, a pulse or train of pulses comprising thesignal COUNT will produce a COUNT UP or COUNT DOWN pulse train when theENABLE signal is present, depending upon the condition of the signalSIGN.

The sign and count logic 405 also includes a sign logic circuit 433 towhich are applied the outputs from the scanning carriage assemblytachometer 23. The sign logic 433 is merely a phase comparator andprovides an output labelled TACH SIGN, which comprises a signal ineither one of two stages depending upon the direction of rotation of themotor 70a. One of the two outputs from the tachometer 23 is coupled to agate 434 where it is gated with the clock signal CL2 and the gatedoutput is coupled as an input to each of a pair of gates 435 and 436.Another input to each of these gates is the signal ENABLE. The TACH SIGNsignal is coupled directly as an input to gate 435, and coupled throughinverter 437 to gate 436. Accordingly, a train of tach pulses willproduce an output train of pulses from either servo up or servo downgates 435, 436, respectively, each occurring at clock time CL2 andselected by the condition of the signal TACH SIGN. The output of gates430, 431, 435 and 436 are coupled as inputs to gates 438 and 439,respectively, in a manner such that signals representing desired upcounts are coupled to gate 438 and the signals representing desired downcounts are coupled to gate 439. These gates are also responsive tosignals BIAS DOWN and BIAS UP, and the production of these signals willnow be explained.

The BIAS UP or DOWN logic 425 is also illustrated in FIG. 14, andincludes a decoder 440, which is responsive to the signals in themicroprocessor address bus and the R/W. Upon detection of a selectedaddress, the decoder 440 provides an input to a gating circuit 441 whereit is gated with the clocking signal CL1 and provides an input to a pairof NAND gates 442 and 443, respectively. The other input to these gatesare provided by different signals from the multi-bit data bus, forexample, as shown in FIG. 14, bit zero is coupled to gate 443 and bitone is coupled to gate 442. The output of the gates 442 and 443 arecoupled respectively to gates 438 and 439 such that the desired upcounting signals are coupled through gate 438 and the desired downcounting signals are coupled through gate 439. Accordingly, OR gate 438produces an output pulse for each count, servo tach pulse or bias pulsefor which the up/down counter 406 is to count up and correspondingly, ORgate 439 produces a pulse corresponding to each count, tach pulse orbias pulse for which the up/down counter 406 is to count down.

From the preceding discussion of FIGS. 11 through 14, operation of thesecond preferred embodiments should now be apparent. In brief compass,and referring again to FIG. 11, the microprocessor responds to lens tach21 pulses in order to keep track of the position of the lens 9 which isdirectly under operator control, and which is representative of thedesired reduction ratio. When the operator presses the start button, themicroprocessor can select, based upon the desired reduction ratio, aparticular table stored in memory from which the various quantities forsetting the counter 403 are derived so as to effectively control themodulus of the counter 403 and therefore the repetition rate of thesignal COUNT. In an embodiment of the invention actually constructed,only a single table was stored, and other tables were created byarithmetically modifying each entry in the single stored table, based onthe desired reduction ratio to, in effect, create a plurality of virtualtables. In some instances, in addition to this creation of pluralvirtual tables, for certain selected reduction ratios, the up/downcounter 406 was also initially set or the initial position of thecarriage selected by selectively pulsing counter 406. This is effectedby the microprocessor by employing the bias up or down logic 405 to, ineffect, step the counter 406 up or down by the selected amount, for theparticular reduction ratio. In addition to such operation, if required,the latches 404 are also initially loaded; reference to FIG. 13indicates that the initial loading requires 4 memory words, i.e., twomemory words to load the latches 404a and b, and an additional pair ofwords to again load the latches 404a and b after their contents havebeen transferred to the latch 404c by appropriate microprocessorinstructions.

Once the foregoing functions have been accomplished, the microprocessoris enabled to issue the microprocessor start signal (see FIG. 12A). Atthe same time, since the image carrier drum is rotating, the counter 414is continuously cycling. When the counter reaches a count to whichdecoder 415 responds, it latches to partially enable the gate 416 andwhen the unique emitter position is reached, gate 416 is fully enabled,producing the ENABLE signal which enables the interrupt counter 417 tobegin counting, and through gate 424, enables counter 403 to begincounting down for each CL1 pulse. The down counting is thus performed ata rate related to the velocity of the image carrier, and when underflowoccurs, the output COUNT is produced with two effects. In the firstplace, it partially enables gate 422, which is fully enabled on the nextCL1 pulse. At the same time, it partially enables either gate 430 or 431(FIG. 14) depending on the condition of the SIGN signal which, in turn,produces an output from either OR gate 438 or 439 to either up or downcount the counter 406.

The counter 403 is now loaded with the quantity retained in the latch404c, and that quantity is again down counted until a new production ofthe COUNT signal. It should be apparent to those skilled in the art thatthe quantity to which the counter 403 is set determines the modulus ofthe counter or the period between subsequent COUNT signals. On eachoccurrence of the INTERRUPT signal (from counter 417--FIG. 12A), thelatches 404c are loaded from latches 404a and b. The INTERRUPT signalmay also be employed, at the microprocessor, so as to provide forloading of the latches 404a and 404b.

Since the counter 403 counts each quantity loaded therein down to theunderflow condition, it is a simple matter to determine the number ofCOUNT pulses produced by any sequence of quantities loaded into thecounter 403. For each such pulse, the up/down counter 406 will count inthe direction determined by the SIGN signal and thus, the totaldisplacement can readily be determined. The rate at which this movementis accomplished, and the acceleration with which it is accomplished isdetermined by the various quantities loaded into the counter 403, andthe sequence in which those quantities exist in a microprocessor memoryfrom which they are loaded.

The INTERRUPT signal is employed, at the processor, to select a quantityto output on the data bus for loading to the latch 404a or b, a singleinterrupt generating a pair of quantities in succession, one for latch404a, the other for 404b. Since the quantities loaded into latches 404aand b are not immediately used, processor timing is no longer a factorin carriage assembly movement.

While a table may be stored for each possible reduction ratio which hasa plurality of quantities stored, one for each quantity used in arescan-scan cycle, memory area can be saved in a number of ways.Firstly, in a constant velocity phase of movement, the quantity whichthe counter decrements is identical. Thus, the quantity need only to bestored once and the processor merely counts the number of INTERRUPTsuntil a given number is reached, after which a different quantity isoutput on the data bus.

Further memory storage can be saved in that a table of quantities forone reduction mode may be similar but offset from another table by aconstant. In such a case, a single table is stored and, to recreate theother table, a constant is added to each entry in the stored table as itis placed on the data bus.

While the invention has been described with reference to a scanningoptical system, it is equally applicable to a moving document systemwhere the servo motor would drive the document support across stationaryoptics. It is also applicable to scanning lens systems where the servomotor would drive the scanning carriage for the lens. Multiple focussystems could be used with the instant invention as well as single focuslens. Additionally, while the invention is obviously of greater valuewhen used with continuously variable systems, it may be used with singlespeed scanning apparatus or apparatus with only a few scanning speeds.

Importantly, the invention can be applied outside the field ofelectrophotographic copiers to wherever scanning mechanisms are used andwherever servo systems are required to possess accurate acceleration andvelocity profiles in order to obtain highly accurate positionrepeatability. Such modifications are uses are well within the skill ofthe art and fall within the scope of the invention.

What is claimed is:
 1. A scanning electrostatic copying machine forcopying at substantially any reduction ratio within a range of reductionratios including:a motor (10), image carrier means (13) driven by saidmotor for recording a latent optical image thereon, a transparentdocument support (50), a lens (9), reduction means (18) for positioningsaid lens between said support and said image carrier means at aposition corresponding to a selected reduction ratio within said range,scanning carriage means (12) including a scanning carriage for scanningsaid document support and for directing an image beam from said documentsupport through said lens to said image carrier means, and servo motormeans (70, 17, 70a) responsive to said reduction means and to motion ofsaid image carrier means for driving said scanning carriage for movementin relation to motion of said image carrier means uniquely selected inaccordance with said selected reduction ratio, said servo motor meansincluding control means (15) for positioning said scanning carriage,preparatory to a document support scanning movement, from a referenceposition to a start of scan position selected in accordance with saidreduction ratio.
 2. The machine of claim 1 in which said servo motormeans includes control means (15) for driving said scanning carriage ata unique velocity relative to motion of said image carrier means duringdocument support scanning movement, said velocity selected in accordancewith said reduction ratio.
 3. The machine of claim 2 in which saidcontrol means (15) further includes a phase locked loop includingfirsttransducing means (22) providing an output representative of imagecarrier means velocity, second transducing means (23) providing anoutput representative of scanning velocity, means for differencing aconstant times said first transducer output and said second transduceroutput (104, 105) and providing an output representative of saiddifference, and means for adjusting scanning carriage velocity (106,107, 109) to reduce said output representative of said difference. 4.The machine of claim 3 in which saidfirst and second transducing meansprovide first and second pulse outputs of frequency corresponding toimage carrier means and scanning carriage velocity, respectively,dividing means (104) clocked by said first pulse output for dividing bya constant selected in dependence on said selected reduction ratio, andsaid means for differencing comprises a phase comparator (105)responsive to said dividing means and said second pulse output.
 5. Themachine of claim 1 in which said servomotor means includesa servomotor(70a), energization means (108, 111, 112, 109) to energize saidservomotor with energization selected in dependence on image carrierposition.
 6. The machine of claim 5 in which said servomotor meansfurther includesacceleration means (112, 111, 100) responsive to saidenergization means to accelerate said scanning carriage for a selectedtime to a unique velocity, said selected time and unique velocityselected in accordance with said selected reduction ratio.
 7. Themachine of claim 6 in which said acceleration means includestiming means(216, 217, 215) enabled on acceleration of said scanning carriage toproduce a series of time spaced pulses, transducer means (23) responsiveto scanning carriage movement to emit an output signal representativethereof, a counter (209, 210) coupled to said transducer means andresponsive thereto, comparison means (111) coupled to said counter andenabled on each of said timing means pulses for comparing a condition ofsaid counter with a desired condition of said counter and for producingan output representative of a difference therebetween, and means (100,107, 109, 110) for applying a signal representative of said differenceto said servomotor.
 8. The machine of claim 7 which furtherincludesmeans (111) for disabling said acceleration means in response tosaid timing means.
 9. The machine of claim 1 which furtherincludesvelocity control means (104, 105) for maintaining scanningcarriage velocity to a selected ratio of image carrier means velocity,selected in accordance with said reduction ratio, acceleration controlmeans (111, 100) for accelerating said scanning carriage for apredetermined time, said predetermined time selected in accordance withsaid selected reduction ratio, means responsive (108, 111) to imagecarriage position for enabling said acceleration control means, and,timing means (215-217, 111) for disabling said acceleration controlmeans and for enabling said velocity control means after a predeterminedacceleration time, predetermined in accordance with said selectedreduction ratio.
 10. The apparatus of claim 1 furtherincludingdeceleration means (111, 112) for decelerating saidservomotormeans when enabled, means responsive to scanning carriageposition (203, 204, 214) for disabling said deceleration means, andposition error means (201, 202, 218, 219, 220, 221) enabled ondisablement of said deceleration means for driving said servomotor meansin accordance with scanning carriage position error.
 11. The apparatusof claim 10 includinga first counter (203, 204) means containing a countrelated to scanning carriage position error, a second counter means(209, 210) containing a count representing scanning carriagedeceleration movement wherein said deceleration means includescomparison means (213) for comparing said first and second counter meansand decelerating said servomotor means when said counts are in apredetermined relation.
 12. The apparatus of claim 10 in which saidmeans for disabling said deceleration means includes a comparator (214)comparing said first counter means to a reference quantity for disablingsaid deceleration means in response to a predetermined relationship ofsaid first counter means and said reference quantity.
 13. The apparatusof claim 10 in which said position error means includesfirst countermeans (201, 202) containing a count related to scanning carriageposition error, and a digital to analog converter means (221) forconverting an output of said first counter means, when enabled, and forapplying said converted output to said servomotor means.
 14. Asubstantially continuously variable reduction ratio document copiermachine with scanning carriage means driven in servo relationship toimage carrier means including:a motor, image carrier means driven bysaid motor for recording an image thereon, scanning carriage means forscanning a document to be copied, servo motor means for driving saidscanning carriage means for scanning movement in synchronism with themotion of said image carrier means, said servo motor means including acontrol means for driving said scanning carriage means at a uniquevelocity relative to the motion of said image carrier means during ascanning movement, wherein said control means includes: firsttransducing means providing a pulse output with frequency representativeof image carrier means velocity, second transducing means providing apulse output with frequency representative of scanning carriage meansvelocity, means for differencing a constant times said first transducingmeans output and said second transducing means output and providing anoutput representative of said difference, said means for differencingincluding: dividing means clocked by said pulse output of said firsttransducing means for dividing by a constant selected in dependence onsaid selected reduction ratio, and a phase comparator responsive to saidpulse output of said second transducing means and said dividing means,and means for adjusting scanning carriage means velocity to reduce saidoutput representative of said difference.
 15. The machine of claim 14 inwhich said servo motor means includes control means for positioning saidscanning carriage, preparatory to a scanning movement, from a restposition to a start of scan position.
 16. A document copier capable ofsubstantially continuous variable reduction ratio with scanning carriagemeans driven in servo relationship to image carrier means including:amotor, image carrier means driven by said motor for recording an imagethereon, scanning carriage means for scanning a document to be copied,servo motor means for driving said scanning carriage means for scanningmovement in synchronism with the motion of said image carrier means,said servo motor means including, a servo motor, and energization meansto energize said servo motor with energization selected in dependence onimage carrier position.
 17. The machine of claim 16 in which saidservomotor means further includes:acceleration means responsive to saidenergization means to accelerate said scanning carriage for a selectedtime to a unique velocity, said selected time and unique velocityselected in accordance with said selected reduction ratio.
 18. Themachine of claim 17 in which said acceleration means includes:timingmeans enabled on acceleration of said scanning carriage to produce aseries of time spaced pulses, transducer means responsive to scanningcarriage movement to emit an output signal representative thereof, acounter coupled to said transducer means and responsive thereto,comparison means coupled to said counter and enabled on each of saidtiming means pulses for comparing a condition of said counter with adesired condition of said counter and for producing an outputrepresentative of a difference therebetween, and means for applying asignal representative of said difference to said servomotor.
 19. Themachine of claim 18 which further includes:means for disabling saidacceleration means in response to said timing means.
 20. A documentcopier capable of substantially continuously variable reduction ratiooperation with scanning carriage means driven in servo relationship toimage carrier means including:a motor, image carrier means driven bysaid motor for recording an image thereon, scanning carriage means forscanning a document to be copied, servo motor means for driving saidscanning carriage means for scanning movement in synchronism with themotion of said image carrier means, wherein said servo motor meansincludes: velocity control means for maintaining velocity of a scanningcarriage in said scanning carriage means relative to image carrier meansvelocity, a ratio of said velocities selected in accordance with saidreduction ratio, acceleration control means for accelerating saidscanning carriage for a predetermined time, said predetermined timeselected in accordance with a selected reduction ratio, means responsiveto image carrier position for enabling said acceleration control means,and timing means for disabling said acceleration control means and forenabling said velocity control means after a predetermined accelerationtime, predetermined in accordance with said selected reduction ratio.21. A document copier capable of substantially continuously variablereduction ratio with scanning carriage means driven in servorelationship to image carrier means including:a motor, image carriermeans driven by said motor for recording an image thereon, scanningcarriage means for scanning a document to be copied, servo motor meansfor driving said scanning carriage means for scanning movement insynchronism with the motion of said image carrier means, wherein saidservo motor means includes: deceleration means for decelerating saidservo motor means when enabled, means responsive to position of ascanning carriage in said scanning carriage means for disabling saiddeceleration means, and position error means enabled on disablement ofsaid deceleration means for driving said servo motor means in accordancewith scanning carriage position error.
 22. The machine of claim 21including:a first counter means containing a count related to scanningcarriage position error, a second counter means containing a countrepresenting scanning carriage deceleration movement wherein saiddeceleration means includes comparison means for comparing said firstand second counter means and decelerating said servomotor means whensaid counts are in a predetermined relation.
 23. The machine of claim 22in which said means for disabling said deceleration means includes acomparator comparing said first counter means to a reference quantityfor disabling said deceleration means in response to a predeterminedrelationship of said first counter means and said reference quantity.24. The machine of claim 23 in which said position error meansincludes:first counter means containing a count related to scanningcarriage position error, and a digital to analog converter means forconverting an output of said first counter means, when enabled, and forapplying said converted output of said servomotor means.
 25. A documentcopier machine with scanning carriage means driven in servo relationshipto image carrier means including:a motor, image carrier means driven bysaid motor for recording an image thereon, scanning carriage means forscanning a document to be copied, servo motor means for driving saidscanning carriage means for scanning a movement in synchronism with themotion of said image carrier means, said servo motor means including afirst closed loop control means to accelerate said scanning carriagemeans from a rest condition towards a desired speed before reaching astart of image transfer position, and second closed loop control meansfor maintaining said scanning carriage means at a constant speed,relative to said image carrier means, throughout said scanning, saidfirst closed loop control means for decelerating said scanning carriagemeans and third closed loop control means for moving said scanningcarriage means to a reference position.
 26. The machine of claim 25which includes means to control said first and second closed loop meansin dependence on a selected reduction ratio within a range of reductionratios.